Emergency vehicles, such as fire-fighting engines, ambulances and police cars, generally have the need to cross or pass intersections under the control of traffic signals. This must be accomplished in the least amount of time possible so that the function of an emergency vehicle can be successfully fulfilled. It is generally understood that the more quickly an emergency vehicle can reach the scene of an emergency, the greater are the chances that the victims involved can be helped or successfully treated.
Since the earliest times, emergency vehicles approaching intersections have depended upon sirens, horns, bells or other types of audible and/or visible warning devices to alert other people in the intersection. This has not always proven to be a successful technique, even though it is still the standard mode of operation for emergency vehicles today. Unfortunately, accidents involving emergency vehicles often occur at intersections due to confusion, impaired hearing, inattention, noise conditions or overly-aggressive drivers seeking to clear the intersection before the arrival of the emergency vehicle. Other factors are the speed of the emergency vehicle and the resulting inability of others to react to it, distractions affecting the driver of the emergency vehicle, and the like. Further problems are caused when multiple emergency vehicles are approaching the same intersection. This situation is further complicated when the sirens and other signals from multiple emergency vehicles can be heard within the same area--a combination confusing to both pedestrians and other motorists, as well as the operators of both emergency vehicles. In many cases, due to siren noise and the intensity of focused driving at high speeds through congested areas, emergency vehicle operators are often not aware of other such vehicles in the same area.
There have been many systems proposed to address these problems. One such system is disclosed in U.S. Pat. Nos. 3,550,078 (re-issue no. 228,100, re-issued Aug. 6, 1974 to Long). The system disclosed provides the ability of an emergency vehicle with the ability to remotely control traffic light signals so as to provide signals that will allow the emergency vehicle to easily pass through intersections without undue delays. Unfortunately, this system does not properly alert pedestrians or other drivers at the subject intersection that the traffic light control has been preempted. Further, there appears to be no means in this system to reconcile control between competing emergency vehicles. Consequently, this system does not compensate for the inattentiveness of pedestrians or other drivers in the intersection. Nor does this system compensate for the approach of other emergency vehicles to the controlled intersection.
Part of this problem has been addressed in U.S. Pat. No. 4,704,610 to Smith et al. This patent discloses a system in which a display at the intersection indicates that preemption of the traffic signal has been carried out and that the emergency vehicle is approaching. This system also indicates whether the emergency vehicle has already passed through the intersection. The signal from the emergency vehicle is transmitted to the controller at the intersection by means of infrared radiation. Consequently, the range of the system is limited. Further, the system does not provide for reconciliation by attempts to control the intersection by two approaching emergency vehicles. Nor does this system advise the operators of emergency vehicles that other emergency vehicles may be in the same area.
Determining priority between emergency vehicles is carried out in the system disclosed by U.S. Patent No. 4,914,434 to Morgan et al. In this system a controller located at a particular intersection carries out a series of computations based upon signal analysis of competing, incoming emergency vehicles, and then selects which emergency vehicle will be given priority. Accordingly, the selected emergency vehicle is provided with a green light while any competing emergency vehicles are advised that they do not have priority through the intersection. The system also encompasses the selection of alternative routes or pathways that an emergency vehicle can take if it has been preempted from control at a particular intersection. Unfortunately, indication that an emergency vehicles control of an intersection traffic signal has been preempted often occurs after it is too late to select alternative routes. In some cases, such indication may not be noticed by the vehicle operator until the emergency vehicle is in the intersection, thereby greatly increasing the risks of accidents between emergency vehicles.
Accordingly there is a need in this technology for a system which advises emergency vehicle operators of other emergency vehicles in the area. Further, information regarding the direction of the other emergency vehicles is needed so that advanced planning can be carried out by the emergency vehicle operator to avoid collisions at intersections, as well as competition for control of traffic signals at intersections. Proper advanced warning for emergency vehicle operators would facilitate greater safety for emergency vehicle operators, pedestrians and other vehicle operators.